The prior art shows that multiple attempts have been made to muffle the sound of vacuum cleaning apparatus from blower-motor units by considering the exhaust noise caused by the working air of the vacuum cleaner such as described in Canadian Pat. No. 1,122,761
The same principle applies to the vacuum cleaner described in Canadian Pat. No. 1,142,716 which uses a sound insulating device at the outlet of the working air i.e. at the outlet of the suction unit.
In Canadian Pat. No. 595,301, Wall has attempted to reduce the noise produced by a dynamo-electric machine by mounting a sound absorbent device adjacent the fan. However, the sound absorbent device has a totally different concept and operates on principles distinct from the present invention.